Quarter-turn fastener assemblies are well known in the prior art. In such fastener assemblies, one of the members to be joined rotatably supports a shaft having a head at one end and having a locking element adjacent its other end. The other of the two members to be joined is formed with a receptacle having an opening registering with an opening in the first member to permit the insertion of the shaft and locking element in one position of the shaft around the axis of rotation. From such an inserting position the shaft can be rotated so that the locking element turns to a locking position in which it is retained by the receptacle.
Quarter-turn fastener assemblies of this type have several disadvantages, one of which is their failure to provide any means for aligning the locking element prior to its insertion in the mating receptacle. Thus, fasteners which nominally act over an angle of about 90.degree. in practice must be turned first, to align the locking element for insertion in the receptacle and, secondly, to move the locking element into a locking position after insertion in the receptacle. Another disadvantage is that the locking element may damage the mating surface or sealing gasket if the members to be joined are not in register. This problem is particularly severe in installations in which a plurality of fasteners are employed to assemble a panel on a flange opening. Another disadvantage is that the fastener elements in these assemblies do not operate correctly to position the parts to be joined, but require separate pilot pins to perform this function.